CMH vs. LED
Which Grow Light is Best for You?

Grow lights have evolved from heavy magnetic, in-efficient ballasts and bulky reflectors to ultra-efficient dimmable and spectrum tunable Light Emitting Diodes (LED) and Ceramic Metal Halide (CMH) all-in-one fixtures. The modern hobby and commercial cultivator now have the power to dial in spectrums specific to the plant strain they are growing. LED’s offer the tunability to go from a vegetative blue spectrum to a flowering red spectrum with a turn of a knob. CMH’s closely mimic the sun, provide the highest gram per watt, and even provide the coveted good UV wavelengths that fend off mold and mildew as well stimulate plant vigor and greater resin and terpene production. Choosing which technology is right for you depends on the size of your grow, how long you will be growing in the space, and your allocated budget.

The anticipated duration of your cultivation project is one of the most important factors to consider. Choose LED if you plan on keeping the fixtures for more than 5 years as the high upfront initial cost of LED fixtures will be amortized over a longer period of time. LED bulbs last 50,000 hours compared to 20,000 for CMH. If you are planning for obsolescence and want the greatest yield ROI within 1-2-year time frame, choose CMH. And even if you keep your grow space past 5 years, don’t worry, CMH’s provide a greater gram per watt due to their higher PPF and canopy penetration.

Let’s talk about the size of your grow. Because of the lack of overall canopy penetration, you will need to keep your LED lights 12-18” above your canopy. This could be a good thing if your ceiling height is less than 8ft and really need to factor in heat management. If you have a larger and taller space, using CMH technology is a better choice. Increased ceiling height allows for better heat management, better air-flow capability and more even light coverage for fuller and taller flower strains. LED lights put off very little heat and this can be good or bad depending on the size of your grow space and the climate at your facility location. How insulated your space is during winter months is crucial if you are operating in colder climates. Due to the lower heat output of LED’s, heat may need to be added to the grow room in colder months which will increase costs. CMH fixtures put off more heat than LED’s, but less heat than their HPS counterparts. This heat can be utilized to achieve the ideal temperature for your growing methodology, for example, if you are using CO2 injection.

 

Finally, everyone’s favorite factor to consider, BUDGET! The initial cost of an LED is 2 to 4 times the cost of a comparable CMH fixture. (see Table 1 below) LED fixtures, especially the ones that include the UV spectrum, are very expensive in terms of up-front cost. When it comes to power consumption and the power bill, LED’s only save the grower about 15% on the power bill compared to CMH fixtures. However, the LED grower will use less power for cooling, but that savings depends on other factors in the grow space. The additional cost a CMH grower will realize is replacing bulbs. You will be buying replacement CMH bulbs after 12-18 months of use. In addition, it is recommended that you change between the 4100K CMH bulbs in the vegetative phase to the 3100K CMH bulbs for flowering. Therefore, you will incur the cost of more bulbs utilizing CMH technology, but you will optimize your light cycles and extend the timeframe to replace bulbs.

In conclusion, each technology, CMH and LED, are viable to successful grows however they speak to different methodologies and business initiatives.

Choose CMH if:

  • You need to maximize ROI in within 1-2 years
  • You need greater canopy penetration for the strains you are growing
  • Need the beneficial UV spectrum for maximum terpene resin production
  • Need to maximize your gram per watt and flower quality
  • Qualify for state rebates

Choose LED if:

  • Have a long-term plan with current LED technology
  • Need an exact spectrum wavelength to grow a specific strain
  • Qualify for state rebates
  • Yield quality and quantity are not paramount

9 Responses

  1. I have a 315 cmh and I’m going to try auto flower for the first time, can I have my 315 and ran a red LED in addition to the 315? In a 5×5 grow tent

    1. Yeah, you can do that. There is range in which a plant’s needs are best met. Adding more light may help marginally, but don’t expect wonders. Also, keep an eye on temperatures at the canopy. Let us know how it works out!

  2. Tried a 315 cmh for a few runs. It’s better than HPS but for my space, I liked the LED much better. I run UBA/B with my led and it outperformed teh chm. New tech is not always better.

      1. Good question. We were forced to remove the charts from this article a while back. An LED company was not happy about it… and sent a letter from their lawyer to us.

        If I remember right, we were comparing 1000w LEDs to CMH.

        K

  3. false… there is no way that CMH gives better results than LED results per true watt. I get better than 3 grams per watt with my LED, and me being a fairly newb grower. CMH can’t touch today’s LEDs. Game over.

  4. @bill Jones while your gram per watt is impressive a experienced grower with the right strain can get that with any of the lights available. I’ve been growing for 20 years and I use leds currently and while they are awesome at saving power etc I get no better gpw with using the leds vs cmh vs hps. For you to state your opinion as fact and say your fairly new shows your lack of experience. Fact is I use a very high priced led to get the same quality and yield I get with a cmh and or hps the difference is my overall cost of running multiple lights. Back to the comment of yield I’ve yielded more with hps and say Santa Cruz blue dream then I have with a solid og kush no matter the light being used genetics play the role as well as experience and quality of lights being used. The info you give is False hope for someone to say hey this amazon led is 100.00 it’ll out perform a 150 vivosun cmh 315 with a Philips bulb and I’m sorry that’ll never happen. Quality leds do yield close to the same as hps and cmh but everything is subject to the basics 1. Grower experience 2. Strain 3. Style (method of growing) 4. Co2 added

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